Python cv2视频捕获仅捕获1帧

Question

我在使用 cv2 VideoCapture 时遇到问题。 MP4 文件在每个文件中仅打印出 1 帧， 我该如何解决？没有错误，文件也没有损坏。

while(cam.isOpened()):
 fname_vid='AlucardMovelogVid_'+str(date.today())+'.mp4'
 out=cv2.VideoWriter(fname_vid,fourcc, 20.0, (640,480))
 now=datetime.now()
 dt_string=now.strftime('%d/%m/%Y, %H:%M:%S : ')
 ret,frame1=cam.read()
 ret,frame2=cam.read()
 diff=cv2.absdiff(frame1,frame2)
 appended_diff=dt_string+str(diff)
 gray=cv2.cvtColor(diff,cv2.COLOR_RGB2GRAY)
 blur=cv2.GaussianBlur(gray,(5,5),0)
 frame=cv2.flip(blur,0)
 movelog.append(appended_diff)
 fname='Alucard_Movelog_'+str(date.today())+'.txt'
 with open(fname, 'w') as file:
     for item in movelog:
         file.write("%s\n" % item)
 out.write(frame)
 if(cv2.waitKey(10)==ord('*')):
    break
 cv2.imshow('Alucard',blur)

out.release()